This prevents experiments with Spooner's ideal complexion (4,3)
I believe the answer is:
test ban
'this prevents experiments with spooner's ideal complexion' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for test ban that I've seen before include "ignorant students might favour?" , "Agreement on limiting nuclear research" , "Prohibition on trying out atomic bombs" , "Battens (anag.)" , "Check on risky race" .)